in Number Theory. Classic cryptographic algorithms rest
on number theory, where abstract mathematical problems are presented
and algorithms to solve them are discussed. These mathematical preliminaries are then
-used to ensure secure encryption of secret messages. We prove
-formal correctness by considering concrete implementations and
-use the recently developed verification system {\rm RISCAL} to
-prove exactness of the treated algorithms. We present the theories
-developed in {\rm RISCAL}, and put them into context of formal verification
-systems.
+used for concepts to ensure secure encryption of secret messages. Popular examples are the
+Diffie-Hellman-key exchange as well as the RSA public-key/private-key exchange procedure.
+In its quint essence, the validity and the secureness of this algorithms rests on the fact,
+that there is no efficient algorithm for computing decompositions of numbers into prime
+numbers and the hardness of the discrete logarithm problem. Still, its not hopeless, and one
+can formulate methods, which, for moderate small input, will solve the problems. We will
+formulate and prove formal correctness of algorithms that solve this problems,
+where we use the recently developed algorithm specification and verification system {\rm RISCAL}.
+It can be used, for automatic checking of finite models, and verify invariants as well as
+formulated post-conditions are indeed valid.
\end{abstract}
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